1. Field of the Invention
The invention relates to composite abrasive products or elements comprising an active part formed by a "compact" having a polycrystalline structure and containing grains of ultra-hard material bonded directly together and a hard and refractory carbide support having a metallurgical bond with the compact.
The term "compact" designates a cemented product formed by grains bonded together by bridges created by diffusion of material in plastic condition.
2. Prior Art
Composite cutting products of the above-defined type are already known in which the compact covers the whole of one face of the support or forms an embedded cutting edge (French Patent No. 2,089,415).
Products are also known formed of an annular compact of ultra-hard material (polycrystalline diamond or cubic boron nitride) carried by a face of a carbide support which is also annular (British Patent No. 1,473,664).
Finally, products are known in which the compact, in the form of a ring, is fixed by brazing or clamping in an annular recess of the support, this recess being defined by a surface perpendicular to the axis of the ring and by an internal surface parallel to the axis (European Patent No. 0,019,467).
According to European Patent No. 0,019,467, this arrangement is supposed to have the advantage of reducing the cost of the composite product by a rational use of the abrasive part, limited to a narrow useful peripheral zone extending along the cutting edge. It is true that this arrangement makes it possible to cut out, from the same starting compact, several concentric strips having the same shape and different diameters and locate them on different products by brazing or mechanical fixing. As in the case of the product defined in British Patent No. 1,473,664, advantage is taken of the fact that a composite product consisting of a layer of ultra-hard material is in fact only used along a peripheral strip along the cutting edge. The ultra-hard compact is however not fixed to its support by a metallurgical bond, which means that all the advantages provided by such a bond are lost.
It is impossible to form a true composite product (i.e. in which the compact is manufactured on the support itself and has a metallurgical bond therewith) when the annular compact occupies a recess of the support whose cross-section has a sharp angle. The reason is that the shrinkage of the compact during high temperature and high pressure sintering of a composite would create stresses causing cracking during cooling after sintering and during use of the product, under the effect of the thermal or mechanical stresses which then appear.